1. Field of the Invention
The present invention relates to an optical disc apparatus that plays back data recorded in an optical disc, such as a DVD and a CD, set in the main body.
2. Description of the Related Art
An optical disc apparatus in the related art that plays back data recorded in an optical disc, such as a DVD and a CD, has been in widespread use. As is known, the optical disc apparatus is provided with a pickup head that reads data recorded in the optical disc set in the main body by irradiating a laser beam to the optical disc and detecting reflected light in a photo detector. The pickup head outputs an RF signal, which is a read signal of data recorded in the optical disc. The RF signal outputted from the pickup head contains various frequency components and the level becomes lower for higher frequencies. Also, jitter becomes worse for signals at lower levels. In order to optimize the jitter, a typical optical disc apparatus performs equalize adjustment on the RF signal, which is an output from the pickup head. The equalize adjustment is the processing to cut off components at frequencies higher than a given frequency from the RF signal read from the optical disc as well as to boost the RF signal. Because the data recorded in the optical disc is in the digital form, the jitter can be suppressed sufficiently even when the cutoff frequency of the RF signal for the equalize adjustment is set to a fixed value. However, because abort amount varies considerably with the recording density of data, the signal quality, etc. of the optical disc to be played (the optical disc set in the main body), it has to be set for each individual optical disc set in the main body.
An optical disc apparatus that sets both the cutoff frequency and a boost amount for each individual optical disc set in the main body has been also in widespread use.
The optical disc apparatus in the related art detects the cutoff frequency and a boost amount of an RF signal at which the jitter becomes optimal for an optical disc set in the main body prior to the playback, and then starts the playback of the optical disc. For the playback of the optical disc, the equalize adjustment is performed on the basis of the cutoff frequency and the boost amount detected at this point. Because parameters (the cutoff frequency and a boost amount) used for the equalize adjustment are detected prior to the playback as has been described, the playback of the optical disc is delayed by a time needed to detect these parameters. To solve this problem, JP-A-2004-227697, JP-A-2002-8243 and JP-A-2002-74845 propose methods for shortening the time needed to detect the cutoff frequency and a boost amount used for the equalize adjustment that is performed prior to the playback.
For example, JP-A-2004-227697 proposes a method as follows on the ground that the cutoff frequency is proportional to the rotational velocity of the optical disc whereas a boost amount hardly varies with respect to the rotational velocity of the optical disc. That is, the cutoff frequency and a boost amount at which the jitter becomes optimal are detected before the rotational velocity of the optical disc reaches the rotational velocity during playback. Then, an optimal cutoff frequency at the rotational velocity during playback is computed on the basis of the cutoff frequency detected at this point and the rotational velocity of the optical disc when this cutoff frequency was detected. For a boost amount, the detected boost amount is used intact.
Also, JP-A-2002-8243 proposes a method for making the processing to detect the cutoff frequency and a boost amount of the RF signal simpler to shorten the time needed for this processing. To be more concrete, a boost amount at which the jitter reaches minimal is detected by varying a boost amount while fixing the cutoff frequency. Then, the cutoff frequency at which the jitter reaches minimal is detected by varying the cutoff frequency while fixing a boost amount to the value detected just before. Finally, a boost amount at which the jitter reaches minimal is detected by varying a boost amount while fixing the cutoff frequency to the value determined just before.
Also, JP-A-2002-74845 proposes a method as follows. That is, initial values of the cutoff frequency and a boost amount have been stored previously, and a boost amount at which the jitter reaches minimal is determined by reducing a boost amount from the initial value step by step by a certain quantity while fixing the cutoff frequency to the initial value.